1. A. Bottino, A. M. Longoni andT. Regge:Nuovo Cimento,23, 454 (1962).
2. S. Mandelstam: (preprint).
3. A. Erdelyi, W. Magnus, F. Oberhettinger andF. G. Tricomi:Higher Transcendental Functions, Bateman Manuscript Project. Bateman’s form for the normalization is not manifestly even. Using properties of the ψ-functions easily leads to it, however.
4. E. J. Squires:Nuovo Cimento,25, 242 (1962).
5. M. Gell-Mann: (To be published).